This Application relates to a drum brake having a rack and pinion drive for driving the brake shoes into engagement, and further having an internal slack adjustment mechanism.
Heavy vehicles often use drum brakes for braking rotation of the vehicle wheels. In a standard drum brake, a pair of opposed shoes are pivotally driven into contact with an inner periphery of a rotating drum. A spring biases the shoes back away from the drum.
An actuator is positioned between the two shoes and is moved by an air brake actuator to drive the shoes into engagement with the drum. As an example, an s-cam is often utilized to drive shoes into engagement. The cams are driven through a mechanism that receives input from the air brake actuator, and then drives the s-cam or other actuator to move the shoes. After a period of time, friction linings on the brake shoes wear. With wear the necessary stroke of the brake to achieve the appropriate braking force increases. The air brake actuator is only capable of a particular amount of stroke, and typically a slack adjuster is positioned between the air brake actuator and the brake shoe actuator. The slack adjuster adjusts the amount of movement necessary to achieve adequate braking force by adjusting the relationship between the two actuators as wear occurs.
The known actuators have proven successful. However, it would be desirable to achieve a simpler and more accurate mechanism for driving the brake shoes and for adjusting the brake shoe actuator.